In the field of data processing equipment magnetic recording discs have long been used for providing readily accessible external data storage. Such discs have conventionally been used with suitable drive and recording apparatus and are generally made readily removable from such apparatus. To provide for accurate, high-density recording of data on such recording discs it has generally been found necessary to provide recording and reading heads extending inwardly of the periphery of the disc and spaced a very few thousandths of an inch above the surface of the disc. Because of this close head to disc spacing it is necessary that the surface of the disc be maintained essentially free of external contaminants such as dust and dirt. The presence of even tiny dust or dirt particles on the surface of the disc could result in interference between the dust particles and the disc and recording head, thus resulting in what is commonly known as "head crash". Such an undesirable condition could result in either damage to the recording head or distortion of the data recorded or read.
To maintain the surfaces of these magnetic recording discs substantially free from such contaminants while still providing for access of the recording head to the disc within the cartridge, disc-enclosing cartridges having a variety of recording head access doors and dust seals have been devised. Conventionally, the head access doors have comprised two plastic members, a first member of substantial elasticity attached to and extending across the top of the cartridge and a second member, or outer door, resiliently attached to the first member and extending downwardly across the opening in the side of the cartridge. Conventionally, the first member extending across the top of the cartridge has been rigidly attached at its end opposite the outer door, to the top of the cartridge, the flexibility and resilience of the plastic member enabling it to be deflected upwardly for opening to gain access to the disc within. Also conventionally, the outer door has been attached to the outer extremity of the first member by a flexible resilient device such as a strip of beryllium copper, thus enabling the outer door to be deflectd outwardly away from the edge of a cartridge while resiliently urging the outer door inwardly toward the edge of the cartridge. In such prior art cartridges the lower portion of the outer door has been dimensioned and configured to bring it close to, but out of, engagement with the adjacent portion of the cartridge. To close the cartridge against external contaminants, such as dust, a dust seal has conventionally been provided in the form of a thin, resilient plastic membrane extending between the lowermost portion of the outer door and the adjacent portion of the cartridge, the resilient urging of the outer door inwardly against the cartridge edge causing this thin plastic membrane to be deflected and thus to effect a dust seal against the adjacent cartridge portion.
Such conventional recording disc cartridges have suffered several significant problems and have been unable to maintain their dust sealing capabilities over an extended period of usage. Among these problems has been a permanent plastic set in the access door first, or upwardly facing, member caused by frequent and sometimes extended deflection of this resilient plastic member during access to the recording disc. When such a set occurs in the access door member, the portion of this member to which the outer door is attached may tend to be bowed upwardly, thus no longer bringing the bottom of the outer door down into dust-excluding contact with the cartridge. Additionally, the non-pivoting, deflecting type of hinge joining the outer door to the transversely extending door may also fatigue or take a set such that the outer door is no longer adequately urged inwardly toward the cartridge to effect the desired dust seal. Yet another problem arises from the thin membrane-type seal used at the bottom of the outer door. As with the other plastic members, this membrane, after prolonged engagement with the adjacent cartridge portion and especially under conditions of elevated temperature, may also take a set such that its previous resilience no longer functions to urge the membrane firmly against the cartridge, as is required to form a proper dust seal.
Another problem encountered by conventional disc cartridges as related to the selectively positionable reset button provided in the lower surface of the cartridge to protect against accidental erasure and unintended recording on the disc. In the conventional cartridge the reset button has been configured such that it may assume an extended, or protecting, position only when located in one of two relatively precise rotational positions. If the button is pressed inwardly and rotated to any position other than such two relatively precise locations, the button will tend to remain in its retracted, non-protecting position. Thus, accidental contact of the button may unintentionally cause it to assume its unprotected position, permitting unintended erasure of previously recorded data.